1. Field of the Invention
The present invention relates to a sheet supply apparatus capable of supplying sheets while automatically correcting an oblique feeding thereof and a recording apparatus such as a printer using the sheet supply apparatus.
2. Description of the Related Art
A printer includes a printing head supported on a carriage and a platen opposed to the printing head. A sheet is conveyed between the printing head and the platen by a pair of sheet conveying rollers, and printed by the printing head. The sheet can be supplied toward the sheet conveying rollers automatically or manually. The sheet conveying rollers are normally stationary, and when a sheet is supplied to the vicinity of the sheet conveying rollers, begins to rotate based on the output of a sensor.
Especially, when a sheet is supplied manually toward the sheet conveying rollers, the problem of oblique feeding of the sheet occurs. The oblique feeding is a phenomenon in which the upper end of the sheet (the leading side of the sheet in the direction of conveyance) is supplied in a diagonal direction to the sheet conveying rollers. When the sheet is supplied to the sheet conveying rollers obliquely, the sheet conveying rollers convey the sheet in oblique position to the printing head, so that the sheet fails to be printed accurately. When the sheet is positioned obliquely when supplied, therefore, the obliqueness of the sheet is desirably corrected.
JP-A-59-108646 discloses an oblique feeding correction apparatus comprising an oblique feeding roller for moving the sheet diagonally to the direction of the sheet conveyance and a side guide. The side guide is arranged on the side end of the sheet conveying path, and the oblique feeding roller causes the sheet to come into contact with the side guide. Thus the sheet proceeds along the side guide so that the oblique feeding thereof is corrected. Further, according to this patent publication, an anti-flexibility member is arranged above the oblique feeding roller and holds the sheet in conveyance from above thereby to prevent the sheet conveyed from being distorted.
JP-A-55-31796 discloses an oblique feeding correction apparatus having two paddle wheels on a shaft. Each paddle wheel has three blades arranged at equal angular intervals and each blade is twisted. The twisted blades move the sheet in a diagonal direction and press it against the side wall of a container. The oblique feeding of the sheet is thus corrected.
JP-A-60-118542 discloses an oblique feeding correction apparatus comprising a common driving roller mounted on a driving shaft and a plurality of driven rollers mounted on two driven shafts arranged on a straight line. The driven shafts are located above the driving shaft and movable in the vertical direction. The driven rollers are pressed against the drive rollers by the weight of the driven shafts and the driven rollers and are thus driven by the driving rollers.
The sheet is held by the driving rollers and the driven rollers and conveyed toward the sheet conveying rollers located ahead. When the sheet is fed obliquely, an upper side end of the sheet (the left side end of the sheet leading in the direction of conveyance, for example) comes into contact with the stationary sheet conveying rollers. Once an end of the sheet comes into contact with the sheet conveying rollers, the sheet slips on the driving roller and the driven rollers in contact (the left end side), so that the sheet continues to be conveyed by the driving roller and the driven rollers on the opposite side (on the right end side). As a result, an end of the sheet stops and the other end thereof is conveyed. Thus, the sheet is rotated about the end thereof in contact with the sheet conveying rollers thereby to correct the oblique feeding of the sheet.
In the conventional oblique feeding correction apparatus in which the oblique feeding of the sheet is corrected by moving the sheet obliquely by a diagonal roller or a twisted blade and bringing it into contact with the side wall of a side guide or a container, even after the sheet comes into contact with the side wall of the side guide or the container and the oblique feeding thereof is corrected, the sheet is subjected to the force from the oblique direction and its movement fluctuates in the direction of conveyance. Thus, the oblique feeding of the sheet fails to be corrected completely.
In the case where driven rollers are arranged on two aligned driven shafts and the sheet slips on the driven roller of one driven shaft while the sheet continues to be moved by the driven roller of the other driven shaft thereby to correct the oblique feeding of the sheet, on the other hand, the sheet slip cannot be controlled as intended. Specifically, the driven roller of one driven shaft and the driven roller of the other driven shaft are configured in the same manner. It is therefore impossible that the sheet slips on the driven roller of one driven shaft and fails to slip on the driven roller of the other driven shaft. Also, in the case where the sheet is conveyed nipped between a driving roller and a driven roller, on the other hand, the sheet is conveyed while being kept nipped between the driving roller and the driven roller and therefore the turning effort for correcting the oblique feeding described above is not generated.
Also, an attempt to forcibly correct the oblique feeding of the sheet exerts an unreasonable force on the sheet and may deform or damage the sheet.